The present invention generally relates to the storage of data using a logical volume pair.
A storage system having a function for backing up data stored in a certain logical volume is known (for example, Japanese Patent Laid-open No. 2003-242011).
For example, a command, which specifies a logical volume, can be issued, and an operations check to determine whether or not processing is being executed normally in accordance with this command, can be carried out. When data is stored in the command-specified logical volume, and an abnormality occurs when processing the command, there is the danger of this data being destroyed. As a method for avoiding this, it is possible to replicate data stored in a primary logical volume (PVOL hereinafter) in a secondary logical volume (SVOL hereinafter) having storage capacity in excess of the storage capacity of the PVOL, and to issue a command, which specifies the SVOL during the above-mentioned operations check.
Subsequent to the operations check, there is no need to keep the data stored in the above-mentioned SVOL, but since this is data which was purposely prepared, it can be saved as a backup of the data stored in the PVOL. However, since the storage capacity of the above-mentioned SVOL exceeds the storage capacity of the PVOL, simply saving the data as-is to this SVOL is a waste of storage system storage capacity.
The above mentioned problem is not limited to an operations check, and may occur in other situations as well.
Further, for example, there is the following data storage mode, that is, a data storage mode in which an SVOL is treated as a virtual logical volume, and a real storage area proportional to the size of the data actually stored in this SVOL is reserved, and this data is stored in this reserved real storage area. However, when the SVOL access frequency is high in this type of data storage mode, there is the danger of storage system performance deteriorating. This is due to the need to search out which real storage area is correspondent to which SVOL virtual storage area.